Check the site (ravensoft.com I believe) and see if they have an executable that will allow the game to run natively on OS X. I know some other games have done that and all you need to do is supply the game files from the original CD.
Nevermind. I just searched Google and went to EpicGames, which has the Unreal titles. Nothing there stating Unreal for Macintosh, even though it's showing the Apple icon.
As far as I know, there is no Unreal app or patch for OS X. The only one done was Glenda Adams (co-founder of Westlake Interactive, moved to Aspyr) for Unreal Tournament. And it never really got developed fully and was unofficial. It required the Mac version of the game CD to work.
Unless you have an older OS 9 bootable Mac, not much you can do.